Heat exchanger

ABSTRACT

A heat exchanger  10  includes a conduit  12  for conveying cooling fluid relative to a body to be cooled. A heat transfer arrangement  62  is arranged in communication with an interior of the conduit  12,  the heat transfer arrangement  62  and the conduit  12  together defining an assembly that is mountable adjacent the body to be cooled, convective heat exchange occurring, in use, due to movement of the cooling fluid relative to the body and to the heat transfer arrangement  62  of the assembly and radiant heat exchange occurring between the body and at least part of the heat transfer arrangement  62  of the assembly.

RELATED APPLICATION

This application is a continuation of U.S. Utility patent applicationSer. No. 13/013,924, filed Jan. 26, 2011 and U.S. Utility applicationSer. No. 11/568,966, filed Aug. 10, 2007, now U.S. Pat. No. 7,901,617,issued Mar. 8, 2011, a national stage filing under 35 U.S.C. 371 ofInternational Application PCT/NZ2005/000101 filed May 16, 2005, whichclaims priority from New Zealand Application No. 533006 filed May 18,2004. The entire teachings of the referenced applications areincorporated herein by reference. International ApplicationPCT/NZ2005/000101 was published under PCT Article 21(2) in English.

BACKGROUND

1. Field

This invention relates to a heat exchanger. The invention relatesparticularly, but not necessarily exclusively, to a heat exchanger foruse in the cooling of furnaces of metalliferous smelters. It willreadily be appreciated that the heat exchanger could be used in a widerange of other applications as well.

2. General Background

In metalliferous smelters and, in particular, aluminium smelters, thesmelter comprises a plurality of pots or furnaces, each having a shellwithin which an electrolyte and molten metal are contained. Aluminium isproduced by an electrolysis process and the temperature of theelectrolyte can reach temperatures of approximately 1000° C. Thisresults in substantially elevated temperatures on the shell of each pot.It is therefore necessary to reduce the temperature of these shells toprotect the shell from corrosion and catastrophic failure.

In the past, this has been achieved by directing a cooling fluid, suchas air, on to the shell at locations which have become excessively hot.This requires very large amounts of compressed air, is extremelyinefficient and generates noise and dust hazards for the operators.Moreover, the air can only be applied in this way to the overheatedlocalised parts of a furnace shell. The shell temperature for the greatmajority of furnaces is not cooled by this means and no overall smelterbenefit is derived.

In another development (U.S. Pat. No. 6,251,237 to Bos et al), theinstallation of permanent ducting as an integral part of each shell hasbeen proposed. Not only does this necessitate a complex conduit systembut some form of forced driving of the fluid is required as well.

In addition, to modify smelters to cool them, it may, in certaincircumstances, be necessary that each furnace first be shut down. Thisis economically disadvantageous as any down time of the smelter hasadverse economic consequences. More importantly, when a furnace is shutdown for any significant length of time, the electrolyte solidifiesresulting in major start up procedures having to be effected in order torestart the furnace.

SUMMARY

According to a first aspect of the invention there is provided a heatexchanger which includes:

a conduit for conveying cooling fluid relative to a body to be cooled;and

a heat transfer arrangement in communication with an interior of theconduit, the heat transfer arrangement and the conduit together definingan assembly that is mountable adjacent the body to be cooled, convectiveheat exchange occurring, in use, due to movement of the cooling fluidrelative to the body and to the heat transfer arrangement of theassembly and radiant heat exchange occurring between the body and atleast part of the heat transfer arrangement of the assembly.

Preferably, the assembly is formed in sections which can be arranged inend-to-end relationship with the conduit forming a passage through whichthe cooling fluid flows as a result of a flue-like effect. With thisarrangement, no moving parts for the heat exchanger are required andheat exchange occurs due to temperature differentials and fluid flowthrough the assembly. At least the heat transfer arrangement is of aheat absorption material and may be a black duct. A “black duct” is tobe understood as a duct which has a high heat absorption characteristic,a low radiant heat reflection characteristic and may be metallic. Toenhance the heat absorption capabilities of the assembly, the metallicduct may be coated with a heat absorption coating such as a black, heatabsorbing paint.

To further encourage heat exchange between fluid in the conduit and thebody of the conduit itself, an operatively inner region of the conduitmay contain heat exchange elements. The heat exchange elements may be inthe form of heat transfer media to effect increased convective heatexchange between the conduit and the cooling fluid within the conduit.

Control of fluid flow through the conduit may be effected by means ofcontrol elements arranged in the conduit. For example, the heatexchanger may include one or more dampers arranged in the conduit forcontrolling flow of the fluid through the conduit.

In a first embodiment of the invention, the heat transfer arrangementmay comprise a plurality of fins arranged on an outer surface of theconduit. Spaces between adjacent fins may serve as radiant heat traps toassist in radiant heat transfer between the body and the assembly. Thefins may be horizontally disposed and vertically spaced. Instead, thefins may be vertically disposed and horizontally spaced, in use, in bothcases to provide an increased surface area to effect convective heatexchange between the body, the cooling fluid and the assembly.

In smelters, electrical power is provided by way of bus bars to thesmelters. In the first embodiment of the invention, the heat exchangermay include a deflector arranged, in use, operatively below the assemblyfor deflecting the cooling fluid into contact with the body to becooled. The deflector may be in the form of a V-shaped (when viewed endon) deflector plate mounted on the bus bars. The deflector plate mayserve to deflect fluid into contact with walls of the bodies. Convectiveheating of the fluid encourages fluid flow up along the sides of thebodies into contact with the assembly. Apertures may be defined in awall of the conduit intermediate the fins so that fluid heatedconvectively by the bodies is drawn into the interior of the conduit tobe entrained therein.

To facilitate placement of the assembly in position relative to thebodies to be cooled, each section of the assembly may be mounted onrollers which, in turn, are supported on the deflector plate.

The heat exchanger may include a fluid entrapment element arrangedoperatively above the conduit for inhibiting escape or by-passing ofheated air. The fluid entrapment element may comprise a hood or coverplate mounted above the assembly which also shrouds the assembly fromdust spillage which may otherwise foul the heat exchanger.

The conduit may taper outwardly towards its downstream end to encouragethe flue-like effect and drag an even flow of cooling fluid into eachsection of the conduit. A downstream end of the conduit is connected toa fluid extraction arrangement of the furnace or structure in which theheat exchanger is contained. For example, in the case of an aluminiumsmelter, the downstream end of the duct may be connected to an extractorfan arrangement of the smelter to provide the force assisted, naturalconvective flow of the fluid through the conduit. Fluid flowing in theconduit may then convectively cool the conduit with a greater flow thanotherwise obtained from a purely natural flue effect.

In certain designs of smelters, space between adjacent cells or furnacesis restricted due to multiple risers which are used for bringing currentinto a following cell or furnace in the line. In a heat exchanger, inaccordance with a variation of the first embodiment of the invention,for use in such smelters, the conduit may be positioned at the level ofor in place of a floor grating arranged above bus bars for the furnaces.

If desired, a heat absorbing accessory is mounted to the conduit, on anunderside of the conduit, mounted in the floor grating. The accessorymay be in the form of a radiant heat capturing element in the form of alens. The lens may “focus” radiant heat from walls of the furnaces on tothe conduit to aid in radiant heat transfer from the walls to theconduit. Instead, the accessory may be in the form of one or morevertical plates for increasing convective heat flow to air which thenflows into the conduit.

In a second embodiment of the invention, the heat transfer arrangementmay comprise a plurality of spaced ducts, connected by a manifold, tothe conduit, the ducts being arranged at spaced intervals along eachmanifold.

Each duct may be in the form of a substantially channel-shaped sectionwhich, in use, is positioned adjacent a wall of the body to form apassage through which the cooling fluid can pass. An entry opening ofeach duct is shaped to reduce a pressure drop associated with entry ofthe cooling fluid into the duct. Further, the duct may connect to themanifold via an exit opening. Each duct may define a secondary exitopening to allow escape of some of the cooling fluid to atmosphere toprovide natural convective flow when no assisted flow is present.

Instead, each duct may be in the form of a tube to be arranged adjacentthe wall of the body to be cooled. Each tube may be substantiallyrectangular in cross-section having a high depth to width aspect ratio.The “width” of the tube may be that dimension of the tube parallel to alongitudinal axis of the manifold and the “depth” of the tube may bethat dimension of the tube normal to the longitudinal axis of themanifold. Thus, the high depth to width aspect ratio of the tube meansthat the width of the tube is substantially less than the depth of thetube. In this way, spaces between adjacent tubes may act as thermalradiation traps to assist in radiant heat transfer.

A part of each tube in proximity to the body may define at least oneaperture to enhance heat transfer between the tube and the body due toreduced thermal boundary layers. The aperture may be a slot extendingparallel to a longitudinal axis of the tube, the slot being defined inthat shorter wall of the slot adjacent the wall of the body in use.

In this embodiment of the invention, the heat exchanger may include ashielding element for shielding those parts of a structure in which thebody to be cooled is located, arranged on an opposite side of theshielding element from the body, from radiation heat transfer from thebody. The shielding element may be in the form of a shield plate which,together with the wall of the body, defines a channel through which thecooling fluid can pass to aid in natural convective heat transfer fromthe wall of the body to those parts of the heat transfer arrangementarranged within the channel.

A rising part of each duct may be arranged in the channel so that heattransfer from the body to the tubes occurs both by radiation and byconvection. Due to the use of the extractor fan, a low pressure regionis created within the heat exchanger to cause fluid flow in the heatexchanger. Convective heat transfer between the fluid in the heatexchanger may therefore be effected as a result of the assisted fluidflow through the heat exchanger.

In a version of this embodiment, each duct may have a vertical sectionentering its manifold via a cranked downstream region of the duct.Cooling fluid may enter the vertical section to be directed into themanifold to effect convective heat transfer.

In another version of this embodiment, each duct may have a horizontalupstream portion leading to a vertical portion arranged between theshielding plate and the body. The transition between vertical andhorizontal portions of the tubes may induce fluid disturbances toinhibit the build up of thermal and hydrodynamic boundary layers toenhance heat transfer. The length of the vertical portion of each tubemay be relatively short further to inhibit the build up of thermal andhydrodynamic boundary layers.

Further, each section of the heat transfer arrangement may comprise aplurality of units, each unit comprising a manifold with its associatedducts, with the manifolds being vertically stacked and the ducts of anupper unit being interleaved with the ducts of a subjacent unitproviding short lengths of vertical portions of the ducts facing thewall of the body to enhance heat transfer.

An interior of each duct may carry surface increasing components toenhance at least one of convective heat transfer rates and radiant heattransfer rates. The components may be selected from the group consistingof fins, vortex inducing elements and combinations of the foregoing.Instead, or in addition, the components may include foraminous elements,such as porous media.

According to a second aspect of the invention, there is provided a heatexchanger which includes at least one duct to be placed in proximity toa body to be cooled, heat exchange between the body and the at least oneduct occurring due to radiant heat transfer between the body and the atleast one duct and due to convective heat transfer to a fluid thatabsorbs heat both from the body and from the at least one duct.

According to a third aspect of the invention, there is provided a methodof cooling a body which includes:

mounting a heat transfer arrangement of a heat exchanger assembly, theassembly including a conduit of a heat absorbing material, in proximityto the body so that radiant heat exchange between the body and at leasta part of the heat transfer arrangement occurs; and

directing cooling fluid past the body, into contact with the heattransfer arrangement and into the conduit so that convective heatexchange between the fluid, the body and the heat transfer arrangementoccurs.

The method may include assisting convective flow of the fluid throughthe heat transfer arrangement and the conduit. Thus, the method mayinclude effecting the assistance by creating a low pressure region in apassage of the conduit, for example, by connecting a downstream end ofthe passage to an extractor fan of an installation in which the heatexchanger is mounted.

This may include forming the heat exchanger assembly in sections andarranging the sections in end-to-end relationship with the conduitforming the passage through which the fluid flows as a result of aflue-like effect.

Further, the method may include effecting increased convective heatexchange between the conduit and the fluid in the conduit by passing thefluid over heat exchange elements contained in the conduit.

In addition, the method may include controlling fluid flow through theconduit by means of control elements arranged in the conduit.

In a first embodiment, the heat transfer arrangement may comprise aplurality of fins arranged on an outer surface of the conduit and themethod may include passing the fluid through spaces between adjacentfins, the spaces serving as radiant heat traps to assist in radiant heattransfer between the body and the assembly.

The method may include mounting the assembly between a plurality ofbodies to be cooled and deflecting fluid into contact with walls of thebodies and drawing the fluid into the interior of the conduit throughapertures defined intermediate the fins in walls of the conduit.

The method may also include arranging a fluid entrapment elementoperatively above the conduit for inhibiting escape or by-passing ofheated air.

Still further, the method may include connecting a downstream end of theconduit to a fluid extraction arrangement.

In a variation of this embodiment, the method may include positioningthe conduit in proximity to a floor of a structure in which the body iscontained. The method may include mounting a heat absorbing accessory tothe conduit.

In a second embodiment, the method may include mounting a plurality ofducts of the heat transfer arrangement at spaced intervals along thebody, adjacent a wall of the body, and connecting a plurality of theducts to the conduit by at least one manifold. Further, the method mayinclude shaping an entry opening of each duct to reduce a pressure dropassociated with entry of cooling fluid into the duct. In addition, themethod may include connecting an exit opening of the duct to themanifold. Also, the method may include providing natural convective flowwhen no assisted flow is present by allowing escape of some of thecooling fluid to atmosphere through a secondary exit opening defined ineach duct.

The method may include enhancing heat transfer between the duct, whichis in the form of a tube, and the body by passing the fluid through anaperture defined in a wall of the tube.

The method may include mounting a shielding element in spacedrelationship relative to a wall of the body for shielding those parts ofa structure in which the body to be cooled is located, arranged on anopposite side of the shielding element from the body, from radiationheat transfer from the body. Then, the method may include passing thefluid through a channel defined between the shielding element and thewall of the body to aid in natural convective heat transfer from thewall of the body to those parts of the heat transfer arrangementarranged within the channel.

The method may include arranging a rising part of each duct in thechannel so that heat transfer from the body to the ducts occurs both byradiation and by convection. Due to the use of the extractor fan, a lowpressure region is created within the heat exchanger to cause fluid flowin the heat exchanger. Convective heat transfer between the fluid in theheat exchanger may therefore be effected as a result of the assistedfluid flow through the heat exchanger.

The method may include enhancing at least one of convective heattransfer and radiant heat transfer by passing the fluid over surfaceincreasing components arranged in an interior of each duct.

DRAWINGS

Exemplary embodiments of the invention are now described with referenceto the accompanying diagrammatic drawings in which:

FIG. 1 shows a schematic, end view of a heat exchanger, in accordancewith a first version of a first embodiment of the invention;

FIG. 2 shows a schematic, three dimensional end view of a heat exchangerin accordance with a second version of the first embodiment of theinvention;

FIG. 3 shows a schematic, side view of part of the heat exchanger ofFIG. 2;

FIG. 4 shows a schematic, plan view of part of the heat exchanger ofFIGS. 2 and 3;

FIG. 5 shows a schematic, end view of a variation of the heat exchangerin accordance with the first embodiment of the invention;

FIG. 6 shows a schematic, end view of a further variation of the heatexchanger in accordance with the first embodiment of the invention;

FIGS. 7-9 show three dimensional views of heat exchangers in accordancewith a second embodiment of the invention;

FIG. 10 shows a three dimensional view of a heat exchanger section of afirst version of the heat exchanger in accordance with the secondembodiment of the invention;

FIG. 11 shows a schematic end view of the section of FIG. 10;

FIG. 12 shows a three dimensional view of another version of a heatexchanger section of the heat exchanger in accordance with the secondembodiment of the invention;

FIG. 13 shows a three dimensional view of one unit of the section ofFIG. 12;

FIG. 14 shows a schematic, end view of the section of FIG. 12;

FIG. 15 shows a schematic, three dimensional view of a part of a heattransfer arrangement of the heat exchanger in accordance with yet afurther embodiment of the invention;

FIG. 16 shows a schematic, sectional plan view of the part of the heattransfer arrangement of FIG. 15;

FIGS. 17A-17C show three variations of entrance openings of the part ofthe heat transfer arrangement of FIG. 15;

FIGS. 18A and B show variations of exit openings of the part of the heattransfer arrangement of FIG. 15;

FIG. 19 shows a three dimensional, schematic view of a first variationof the part of the heat transfer arrangement of FIG. 15;

FIG. 20 shows a schematic, sectional plan view of the part of the heattransfer arrangement of FIG. 19;

FIG. 21 shows a schematic, three dimensional view of a second variationof the part of the heat transfer arrangement of FIG. 15;

FIG. 22 shows a schematic, plan view of the part of the heat transferarrangement of FIG. 21;

FIG. 23 shows a schematic, three dimensional view of a third variationof the part of the heat transfer arrangement of FIG. 15;

FIG. 24 shows a schematic, sectional plan view of the part of the heattransfer arrangement of FIG. 23;

FIG. 25 shows a schematic, three dimensional view of a fourth variationof the part of the heat transfer arrangement of FIG. 15;

FIG. 26 shows a schematic, sectional plan view of the part of the heattransfer arrangement of FIG. 25;

FIG. 27 shows a schematic, three dimensional view of a fifth variationof the part of the heat transfer arrangement of FIG. 15;

FIG. 28 shows a schematic, sectional plan view of the part of the heattransfer arrangement of FIG. 27;

FIG. 29 shows a schematic, sectional side view of another embodiment ofa part of a heat transfer arrangement of the heat exchanger; and

FIG. 30 shows a schematic, sectional plan view of the part of the heattransfer arrangement of FIG. 29.

DETAILED DESCRIPTION

In FIGS. 1 to 6 of the drawings, reference numeral 10 generallydesignates a heat exchanger, in accordance with a first embodiment ofthe invention. The heat exchanger 10 includes a conduit 12 which, inuse, is arranged between two bodies, in the form of furnaces,illustrated schematically at 14, to be cooled. The conduit 12 defines apassage 16.

A heat transfer arrangement in the form of a plurality of spaced fins 18is attached to an exterior surface of the conduit 12. An assemblycomprising the conduit 12 and the fins 18 is referred to below, for easeof explanation, as a duct 20.

In the embodiment illustrated in FIG. 1 of the drawings, the fins 18 arevertically spaced and substantially horizontally disposed or at a slightangle to the horizontal.

The duct 20 is of a heat absorbing material. More particularly, the duct20 is of an aluminium material and is coated with a heat absorbingmaterial to enhance the heat absorption characteristics of the duct 20.For example, the duct 20 is coated with a black, heat absorbing paint.

The passage 16 of the conduit 12 of the duct 20 is connected, at anegress end, to a fluid extraction arrangement of a smelter in which thefurnaces 14 are contained. More particularly, the passage 16 isconnected to an extractor fan (not shown) to create a low pressureregion in the heat exchanger 10 to encourage fluid flow through thepassage 16.

The conduit 12 has a plurality of apertures, illustrated schematicallyat 22, through which air can flow into the passage 16 of the duct 20.

The heat exchanger 10 includes a deflector in the form of a V-shapeddeflector plate 24 arranged beneath the duct 20.

Typically, the furnaces 14 of the smelter are provided with electricalpower by means of bus bars 26. The deflector plate 24 is mounted on thebus bars 26 to deflect air, illustrated schematically at 28, around thedeflector plate 24 into contact with side walls 30 of the furnaces, aswill be described in greater detail below.

A fluid entrapment means in the form of a hood or cover plate 32 ismounted above the duct 20 to trap air 28 and direct it towards the fins18 of the duct 20. The hood 32 also shrouds the heat exchanger 10against dust ingress from above.

A mesh 34 is mounted above the hood 32 so that any air 28 which doesescape can pass through the mesh 34.

As described above, in the embodiment illustrated in FIG. 1 of thedrawings, the fins 18 are vertically spaced. In the embodimentillustrated in FIGS. 2 to 4 of the drawings, in which like referencenumerals refer to like parts unless otherwise specified, the fins 18 arevertically disposed and substantially horizontally spaced.

Referring again to FIG. 1 of the drawings, it is to be noted that theduct 20 is mounted via insulated rollers 36 on the deflector plate 24.

The duct 20 is, preferably, formed in lengths or sections to be wheeledinto position between two furnaces 14 and secured in end-to-endrelationship with an end-most length or section having its downstreamend connected to the extractor fan of the smelter, preferably via theindividual furnace extraction ducts already in place for the furnaces.

To encourage flow of air, as indicated by arrows 38, through the passage16 of the duct 20, the passage 16 flares outwardly towards itsdownstream end, as shown in greater detail in FIG. 3 of the drawings.Also, referring to FIG. 3 of the drawings, it is to be noted that thedeflector plate 24 is mounted via rollers 40 on the bus bars 26 tofacilitate placement of the deflector plate 24 and the duct 20positioned relative to the furnaces 14. The rollers 40 also electricallyinsulate the duct 20 from the bus bars 26.

Referring now to FIGS. 5 and 6 of the drawings, two variations of thefirst embodiment are illustrated. Once again, with reference to FIGS. 1to 4 of the drawings, like reference numerals refer to like parts,unless otherwise specified.

In the design of certain smelters, multiple side risers are used forbringing current into a following cell or furnace in the line. As aresult of these risers, there is very limited room to install the duct20.

In such smelters, the bus bars providing power to the furnaces 14 arearranged below floor level beneath a grating or floor slabs.

In the two variations of the first embodiment illustrated in FIGS. 5 and6 of the drawings, the existing grating for each furnace is replacedwith a new grating 46 with a duct 20 of the heat exchanger 10 mounted inthe plane of the grating 46.

It is envisaged that, with this arrangement, heat transfer between theexternal walls 30 of the furnaces 14 and the duct 20 could occurconvectively without the need for any further heat transfer devices.

However, in the variation shown in FIG. 5 of the drawings, to encourageradiant heat exchange between the walls 30 of the furnaces 14 and theduct 20, an accessory in the form of a lens 48 is mounted on the duct20. The lens 48 encourages radiant heat capture from the walls 30 of thefurnaces 14 to be released into the passage 16 of the conduit 12 of theduct 20.

In the variation shown in FIG. 6 of the drawings, a plate-like accessory50 is attached to the duct 12 to encourage convective heat flow from thewalls 30 of the furnaces 14 into the passage 16 of the conduit 12 of theduct 20.

In use, in the embodiments illustrated in FIGS. 1 to 4 of the drawings,sections of the duct 20 of the heat exchanger 10 are positioned inend-to-end, connected relationship between two furnaces 14 to be cooled.The downstream end of the passage 16 of the duct 20 is connected to theextractor fan of the smelter. This creates a low pressure zone in thepassage and encourages air flow through the passage 16 as indicated bythe arrows 38. A flue-like effect is therefore created in the passage 16of the duct 20. In the embodiments illustrated in FIGS. 5 and 6 of thedrawings, sections of the duct 20 of the heat exchanger 10 and the newgrating 46 are positioned in place of the original gratings. Thesections of the duct 20 are connected together in end-to endrelationship along the length of each furnace 14 to be cooled. Thedownstream end of the passage 16 of the duct is, as is the case inrespect of the other embodiments, connected to the extractor fan of thesmelter to create air flow through the passage 16 of the duct 20.

Cool air from a basement (not shown) of the smelter flows between thefurnaces 14 as indicated by the arrows 28 until it impinges on thedeflector plate 24 where it is forced to diverge into impingement withthe walls 30 of each of the furnaces 14 to be cooled. This creates afirst stage of cooling by fan-assisted, natural, convective heat flow.

Due to the extractor fan drawing air through the passage 16 of the duct20, a low pressure area is created in the passage 16 in comparison withthe exterior of the duct 20. As a result, the air heated by the walls 30of the furnaces 14 is accelerated up the furnace walls 30 and is drawnin, through the apertures 22 of the conduit 12, into the passage 16 asindicated by arrows 42.

Prior to the air entering the interior of the conduit 12 of the duct 20,the air must pass between the fins 18 or between the plate-likeaccessories 50 or through the radiative lens 48, as the case may be.These items 18, 48, 50 absorb radiant heat emitted from the walls 30 ofthe furnace 14 as indicated, for example, by arrows 44 in FIG. 4 of thedrawings. In addition, the relevant items 18, 48 or 50 act as a heatsink for the conduit 12 itself. The air impinging on the items 18, 48,50 cools them convectively in the second stage of heat transfer.

When the air enters the passage 16 of the conduit 12 of the duct 20, itis entrained in the draft and is drawn towards the exit end of thepassage 16. As it passes through the passage 16, the air cools theconduit 12 convectively. To enhance cooling of the conduit 12 of theduct 20, the interior of the conduit 12 has a heat transfer mesh 46, orother heat transfer media, contained therein, as shown in FIG. 1 of thedrawings. This further enhances heat transfer between the duct 20 andthe air passing through the passage 16 to effect cooling of the duct 20and to maintain a sufficient thermal gradient between the duct 20 andthe walls 30 of the furnace 14 so that radiant heat exchange can occurbetween the walls 30 of the furnaces 14 and the duct 20 of the heatexchanger 10.

Referring to FIGS. 7 to 14 of the drawings, a second embodiment of theheat exchanger 10 is illustrated and described. With reference to theprevious drawings, like reference numerals refer to like parts, unlessotherwise specified. In the example shown in FIG. 7 of the drawings, theheat exchanger 10 comprises two banks 60 of heat exchanger sections 62.The heat exchanger sections 62 are connected via duct branches 64 andduct connectors 66 to the conduit 12 defining the passage 16. In theversion shown in FIG. 7 of the drawings, the conduit 12 is maintained atbasement level and exits outside a furnace building out of a work zoneof operators of the furnace. Thus, air heated in the heat exchanger 10is discharged, as indicated by arrow 68, through the passage 16 of theconduit 12.

Referring to FIG. 8 of the drawings, once again, the heat exchanger 10is made up of two banks 60 of heat exchanger sections 62. In thisembodiment, each bank 60 is bifurcated to have two stacks 70, one ateach end of the bank 60, through which heated air is expelled above theoperators' work zone.

Similarly, in the version of the heat exchanger shown in FIG. 9 of thedrawings, the banks 60 are bifurcated to have a stack 70 at each endthrough which air is expelled as indicated by the arrows 68. It is to benoted that the duct 20 in the embodiments shown in FIGS. 5 and 6 couldbe connected to similar stacks 70 to carry heated air away from theworkers' environment.

In the case of the versions in both FIGS. 8 and 9, therefore, the airheated in the heat exchanger 10 is expelled at a region above theoperators' work zone. In all three versions, exposure of the operatorsto heat stress arising from operation of the heat exchanger 10 isreduced.

Referring to FIGS. 10 and 11 of the drawings, one of the sections 62 ofthe heat exchanger 10, in accordance with a first version of the secondembodiment of the invention, is described in greater detail.

In this embodiment of the invention, each section 62 of the heatexchanger 10 comprises a heat transfer arrangement which is in the formof a plurality of spaced tubes 72. The tubes 72 are connected to amanifold 74. The manifold 74 connects the tubes 72 of each section 62 tothe duct branches 64 which, in turn, are connected via the connectors 66to the conduit 12.

Each tube 72 has a high depth to width aspect ratio (as defined). Inthis way, spaces between adjacent tubes act as thermal radiation trapsassisting in the radiative heat transfer process.

Each tube 72 has a vertical or rising part 76 and is connected to itsmanifold 74 via a cranked part 78.

The vertical part 76 of each tube 72 is contained behind a shieldingplate 80. The shielding plate 80 is arranged substantially parallel tothe wall 30 of the furnace 14 to create a channel 82 in which thecooling air 28 rises due to natural convective flow. This naturalconvective heat flow in the channel 82 assists in cooling of the furnace14 and can be of benefit if the forced air flow in the passage 16 of theconduit 12 fails for any reason allowing increased time periods torecommence the force assisted air flow in the passage 16 of the conduit12 of the heat exchanger 10.

It is to be noted that the tubes 72 are located in close proximity tothe wall 30 of the furnace 14. Radiant and natural convection heattransfer mechanisms transfer heat from the wall 30 of the furnace 14 tothe heat exchanger tubes 72. These heat exchanger tubes 72 have a highthermal conductivity and absorb high levels of heat from the walls 30 ofthe furnace 14. As indicated above, the high depth to width aspect ratioof the heat exchanger tubes 72 provide spaces between adjacent tubes 72,the spaces acting as thermal radiation traps which assist the radiativeheat transfer process. In addition, natural convection from the wall 30of the furnace 14 transfers some heat into the heat exchanger tubes 72.

As described above, the downstream end of the conduit 12 is connected tothe extractor fan of the furnace building, the fan creating a lowpressure region in the passage 16. It will appreciated that this alsocreates a low pressure region in all parts of the heat exchanger 10upstream of the passage 16. Thus, the cooling air 28 is drawn into thetubes 72 as shown in FIG. 11 of the drawings. Instead of the downstreamend of the conduit 12 being connected to the extractor fan of thebuilding, a separate fan or fans may be provided for the sole purpose ofextracting the fluid from the heat exchanger 10. A downstream end of theconduit 12 could, instead, be connected to a thermally driven, externalchimney utilising a “stack effect” to provide a low pressure region toencourage air flow through the conduit 12.

This cooling air 28 moves vertically within the heat exchanger tubes 72which have been radiatively heated by the wall 30 of the furnace 14.Heat is transferred from the heat exchanger tubes 72 to the air flowingwithin the tubes 72 via forced convection. The velocity of the airwithin the heat exchanger 10 is such as to cause high rates of heattransfer from the surfaces of the heat exchanger tubes 72 to the air 28flowing in the tubes 72.

To assist in this heat transfer, internal surfaces of each of the tubes72 may include extended surface features (not shown), such as porousmedia, to increase heat transfer rates.

Air 28 exiting the tubes 72 meets the cranked region 78 of each tube 72.This cranked region 78 assists in breaking down thermal and hydrodynamicboundary layers, the breaking down of the boundary layers assisting inpromoting convective heat transfer from the tubes 72 to the air 28.

Referring to FIGS. 12-14 of the drawings, another version of the secondembodiment of the heat exchanger 10 is described. Each heat exchangersection 62 comprises a plurality of units 84, one of which is shown ingreater detail in FIG. 13 of the drawings. Each unit 84 comprises amanifold 74 and a plurality of heat exchanger tubes 72 arranged atspaced intervals along the length of the manifold 74.

In this version of the second embodiment, each tube 72 has a horizontalupstream section 86 feeding into a vertical part 88 which, in turn,feeds into a cranked part 90 prior to entry into the manifold 74.

As shown more clearly in FIG. 14 of the drawings, the vertical part 88of each tube 72 is maintained in the channel 82 between the wall 30 ofthe furnace 14 and the shield plate 80.

Further, in this embodiment, the manifolds 74 of the units 84 arestacked in vertically spaced relationship so that the horizontal parts86 of the tubes 72 of an upper unit 84 are interleaved with the tubes 72of a subjacent unit with the horizontal parts 86 of the tubes 74 beingarranged below the manifolds 74 of the subjacent unit 84.

The manifolds 74 are connected to a downstream manifold 92 having anoutlet passage 94 which connects to the duct branches 64 and, via theduct connectors 66, to the conduit 12.

In this version of the second embodiment of the heat exchanger 10, air28 is drawn into the horizontal parts of the tubes 86 due to the forcedflow in the passage 16 of the conduit 12. The air 28 traverses thevertical part 88 of each of the tubes 72. The change in air flowdirection enhances heat transfer through disturbance of thermal andhydrodynamic boundary layers. In addition, the vertical length 88 isshort relative to the full length of the tube 72. This further enhancesheat transfer by inhibiting build up of thermal and hydrodynamic layersin the vertical parts 88 of the tubes 72.

Referring now to FIGS. 15 to 28, yet a further variation of the secondembodiment of the heat exchanger 10 is described. Once again, withreference to the previous drawings, like reference numerals refer tolike parts, unless otherwise specified.

In this variation of the second embodiment of the invention, eachsection 62 of the heat transfer arrangement of the heat exchanger 10comprises at least one channel-shaped duct 100 (one of which is shown)having a pair of outwardly extending flanges 102. These flanges 102, inuse, are placed against an outer surface of the wall 30 of the furnace14 to be cooled as shown in FIGS. 15 and 16 of the drawings. In sodoing, a passage 104 is formed. The cooling fluid or air passes throughthe passage in the direction of arrow 106.

To encourage heat exchange between the wall 30 of the furnace 14 and theduct 100, internal surfaces of the duct 100 are prepared or coated toprovide a high emissivity surface to encourage heat absorption from thefurnace wall 30. Typically, the duct 100 is of a suitable metal and iscoated with black heat absorption paint to encourage heat transfer.

Radiant heat exchange occurs between the furnace wall 30 and,particularly, the wall 108 of the heat exchanger duct 100 spaced fromthe furnace wall 30. Convective heat exchange occurs due to the passageof air through the passage 104, through an exit opening 110 (FIGS. 18Aand 18B) and into the manifold 74 (not shown in FIGS. 15 to 28). Asdescribed above, the air from the manifold is drawn into the passage 16of the conduit 12 for expulsion from the structure in which the furnaces14 are arranged. Once again, convective heat exchange occurs due toassisted flow of the air through the ducts 100, the manifolds 74 and theconduits 12 by connecting an egress end of the conduit 12 to a suitableextractor fan. Additionally, natural convective flow is enhanced due tothe flue-like effect created by the stacks 70.

An inlet opening 112 of each duct 100 may be square as shown in FIG. 17Aof the drawings. Instead, the inlet opening 112 may be shaped (as shownin FIGS. 17B and 17C of the drawings) to reduce the pressure dropassociated with entry into the duct 100. For a standard, straight edgeentry opening 112, as shown in FIG. 17A of the drawings, the pressureloss coefficient is 1 but may drop to less than 0.1 for a radiused orangled inlet opening (as shown in FIGS. 17B and 17C) having a ratio ofentry radius to hydraulic diameter greater than 0.2.

The requirement for the entry shape is dependent on an optimum betweenthe cost of providing forced flow through the duct 100, the velocity ofthe air through the passage 104 of each duct 100 and the additional costof providing the specific shape.

A single exit opening 110 for each duct 100 may be provided as shown inFIG. 18A of the drawings for connection to the manifold 74 so that allthe cooling air passes into the manifold 74. Instead, as shown in FIG.18B of the drawings, a secondary exit opening 114 can be providedthrough which a part of the cooling air flows, as shown by arrow 116.This partial air flow 116 may be of assistance where, for some reason,the forced convective flow through the ducts 100 ceases for any reason.The air flow 116 maintains natural convective cooling of the wall 30 ofthe furnace 14. This should provide sufficient time to enable remedialaction to be taken to reinstate the forced flow of air through the ducts100 and to reduce the likelihood of significant damage to the wall 30 ofthe furnace 14 occurring.

If desired, the secondary exit opening 114 could be closed off by apressure controlled flap (not shown) which, while there is forced flowof air through the duct 100 is held in a position closing off thesecondary exit opening 114. Loss of pressure due to failure of theforced flow causes the flap to move to a position opening the secondaryexit opening and allowing flow through the secondary exit opening 114.

A fully closed duct as shown in FIG. 18A has the advantage that all theheated air from the sections 62 is removed from surrounds of the furnace14 including the operator working zone. This has the potential forreducing operator heat stress.

The partially open duct 100, as shown in FIG. 18B of the drawings,allows a portion of the heated air to pass into the branches and mainconduit 12 to be removed from the local furnace environment. Asdescribed above, the remaining portion of the air flows, in thedirection of the arrow 116, past the furnace wall 30 to maintain ameasure of convective cooling of the furnace wall 30.

To enhance heat transfer between each section 62 and the furnace wall30, each duct 100 contains heat transfer enhancing surfaces 118. In thevariation illustrated in FIGS. 19 and 20 of the drawings, the heattransfer enhancing surfaces 118 are defined by fins 120 extendingparallel to the direction of air flow through the passage 104 of eachduct 100. These fins 120 do not create a significant pressure drop. Thefins 120 act as heat sinks for accepting radiant and convective heattransfer from the furnace wall 30 and for transferring this heat to thecooling fluid passing through the spaces between adjacent fins 120. Aswith the duct 100, the fins 120 are treated to have high emissivitysurfaces.

In the variation shown in FIGS. 21 and 22 of the drawings, instead ofplanar fins 120, each fin is slotted to provide short length fins 122which are off set with respect to each other to form substantiallyV-shaped structures arranged in a staggered array of short lengths asshown in FIGS. 21 and 22 of the drawings.

This arrangement assists in reducing thermal boundary layers and, in sodoing, enhancing convective heat transfer.

In FIGS. 23 and 24 of the drawings, the heat transfer enhancing surfaces118 comprise vortex generators 124 secured to an inner surface of thewall 108 of each duct 100 to lie within the passage 104, in use. Thevortex generators 124 impede fluid flow through the passage 104 andcause vortices to develop. These vortices, once again, reduce the buildup of thermal boundary layers enhancing convective heat transfer. As afurther enhancement, orifices can be cut into the wall 108 of each duct100, as shown schematically at 126 in FIG. 23 of the drawings. Theseorifices 126 draw cooler fluid into the passage 104 of the section 62further to enhance heat transfer.

Yet a further variation of the heat transferring surfaces 118 is shownin FIGS. 25 and 26 of the drawings. In this variation, the vortexgenerators 124 are arranged at vertically spaced intervals on the fins120. The vortex generators 124 assist in transferring heat from the fins120 to the cooling fluid and serve to maintain the fins 120 at a lowertemperature. This allows both radiant heat transfer from the furnacewall 30 to occur as well as convective heat transfer from the heattransfer enhancing surfaces 118 to the cooling fluid flowing through thepassage 104.

In the variation shown in FIGS. 27 and 28 of the drawings, the heattransfer enhancing surfaces are defined by corrugated fins 128. Inaddition, the fins 128 are perforated. The fins 128 are so arranged toform alternating wider and narrower passages between adjacent fins 128.The cooling fluid moves through these alternating wider and narrowersections creating localised pressure differentials which promote fluidflow through the perforated fins 128.

The combination of the extended surfaces defined by the fins 128, thealternating narrower and wider sections which reduce thermal boundarylayers and fluid flow through the perforations of the fins 128 allenhance heat transfer.

The section 62 shown in FIGS. 29 and 30 of the drawings is a variationof the section 62 described above with reference to FIGS. 10 and 11 ofthe drawings and could also apply to the embodiments shown in FIGS. 12to 14 of the drawings.

In this variation, each tube 72 has a slit 130 defined in the narrowerwall of the tube 72 closer to the furnace wall 30. The slit 130 extendslongitudinally.

A pressure differential is created across the tube 72 to encourage fluidflow in the direction of arrows 132 (FIG. 30). The cooling fluidimpinges on the external surface of the wall 30 of the furnace 14 and isdrawn into the slits 130 of the tubes 72 of each section 62. Thiscooling fluid is then, as described above with reference to FIGS. 10 and11, fed through the manifold 74, into the conduit 12 for extraction. Thefluid impinging on the furnace wall 30 reduces thermal boundary layerswhich enhances heat transfer. Heat transfer is also enhanced by thesupply of cooler fluid external to the heat exchanger sections 62. Thisfluid flow is in addition to the fluid flow through the tubes 72 in thedirection of the longitudinal axis of the tube 72 as described abovewith reference to FIGS. 10 and 11.

While this variation has been described with reference to alongitudinally extending slit, the slits can either be the full lengthof the tube 72 or of short lengths along the length of the tube 72.Another variation would be the use of a plurality of short tubes eachdefining a slit 130 with the tubes being arranged in horizontally andvertically spaced relationship to cover the furnace wall 30. Thisarrangement would be similar to that described above with reference toFIGS. 12 to 14 of the drawings.

An advantage of the second embodiment of the invention is the use ofnatural convective flow outside of the heat exchanger tubes 72. Asindicated above, should forced convective flow in the passage 16 stopfor any reason, the natural convective flow will, the Applicantbelieves, reduce the temperature rise of the wall 30 of the furnace 14enabling remedial action to be taken with the likelihood of damage tothe furnace due to overheating being reduced.

It is a particular advantage of the invention that a heat exchanger 10is provided which uses a single heat exchange fluid. Heat exchangebetween the heat exchanger 10 and the furnaces 14 occurs bothconvectively and radiantly to enhance heat transfer.

A further major advantage of the invention is that a heat exchanger 10is provided which can be mounted in situ without the need for anymodification of the furnaces 14. Thus, the heat exchanger 10 can bemounted in position relative to the furnaces 14 without shutting downthe furnaces 14. Thus, down time of the furnaces 14 is reduced, if notaltogether eliminated, which has major economic benefits.

In addition, the provision of the heat exchanger 10 in lengths orsections facilitates the installation of the heat exchanger 10. Nosignificant modification of the smelter is required apart from, whereapplicable, the installation of a fan system for the heat exchanger 10,which may optionally include a connection of the exit end of the conduit12 to the extractor fan of the smelter.

In regard to the embodiment of the invention illustrated in FIGS. 5, 6and 7-30 of the drawings, it is yet a further advantage of the inventionthat heat loading on operators in the smelter is reduced as heat isdrawn through the conduit 12 and exits remote from the working zone ofthe operators.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A heat exchanger which includes a conduit for conveying heat exchangegas relative to a device; and at least one duct in communication with aninterior of the conduit, the at least one duct, in use, being positionedadjacent an external surface of an external wall of the device to form,together with the wall of the device, a passage through which the heatexchange gas is able to pass, the conduit and the at least one ducttogether defining an assembly that is mountable, in use, adjacent to,and externally of, the device, whereby radiant heat exchange occursbetween the device and the at least one duct and convective heatexchange occurs due to movement of the heat exchange gas relative to thedevice and to the at least one duct, the duct further comprising heattransfer enhancing parts in the form of vortex inducing componentsarranged on an inner side of a wall of the at least one duct to liewithin a flow path of the heat exchange gas in the passage to causevortices to be developed in the heat exchange gas thereby to reduceformation of thermal boundary layers and thereby to enhance at leastconvective heat transfer between the at least one duct and the heatexchange gas.
 2. The heat exchanger of claim 1 in which the duct ischannel-shaped having an open side with the wall of the furnace closingoff the open side to form the passage in use.
 3. The heat exchanger ofclaim 1 in which the heat transfer enhancing parts further comprisesurface area increasing components.
 4. The heat exchanger of claim 3 inwhich the surface area increasing components comprise fins.
 5. The heatexchange of claim 4 in which the fins are shaped to reduce thermalboundary layers.
 6. The heat exchanger of claim 1 in which an orifice isassociated with each of at least some of the vortex inducing componentsfurther to enhance heat transfer.
 7. The heat exchanger of claim 1 inwhich an inlet opening of the at least one duct is shaped to reduce apressure drop associated with entry of the heat exchange gas into aninterior of the at least duct.
 8. The heat exchanger of claim 1 in whichthe at least one duct has a primary outlet opening through which theheat exchange gas enters into the conduit and a secondary exit openingthrough which some of the heat exchange gas can pass to assist innatural convective heat exchange.
 9. The heat exchanger of claim 1 inwhich the heat exchange gas is air.
 10. An assembly comprising a device;and a heat exchanger mounted to the device, the heat exchangercomprising a conduit for conveying heat exchange gas relative to thedevice; and at least one duct in communication with an interior of theconduit, the at least one duct, in use, being positioned adjacent anexternal surface of an external wall of the device to form, togetherwith the wall of the device, a passage through which the heat exchangegas can pass, the conduit and the at least one duct together defining anassembly that is mountable, in use, adjacent to, and externally of, thedevice to be cooled, whereby radiant heat exchange occurs between thedevice and the at least one duct and convective heat exchange occurs dueto movement of the heat exchange gas relative to the device and to theat least one duct, the duct further comprising heat transfer enhancingparts in the form of vortex inducing components arranged on an innerside of a wall of the at least one duct to lie within a flow path of theheat exchange gas in the passage to cause vortices to be developed inthe heat exchange gas to reduce formation of thermal boundary layers andthereby to enhance at least convective heat transfer between the atleast one duct and the heat exchange gas.